THE HOLOCENE LAKE-LEVEL HISTORY OF MARCELLA LAKE, SOUTHERN YUKON TERRITORY, CANADA

The thick Late-Pleistocene mantle of carbonaceous tills and glaciofluvial outwash in the southern Yukon Territory is pockmarked with thousands of closed basin kettle lakes. In the semi-arid rain shadow of the St. Elias Mountains, lake-levels respond to changes in effective moisture if other non-climatic hydrologic variables controlling groundwater flow are negligible. Marcella Lake is a small (<1 km²), closed basin kettle perched on a terrace comprising the northwest perimeter of Atlin Lake (60^o04.422N, 133^o48.475W, elevation 760m). Multi-proxy sediment analyses and radiocarbon age dating of sediment cores from deep to shallow water show multiple Holocene lake-level variations.

Marcella Lake is an oblong shape with a depth of 10m in the center. The bathymetry is a symmetrical depression on all sides but the southwest, where the lake gradually shallows to 1-m depth and a thick charophyte bed covers a flat submerged bay. Sediment cores were retrieved from the deep (10m), shallow (2m) and intermediate (4.4m) depths and were 480, 380 and 205-cm long, respectively. All cores terminate in a gravel diamicton. Radiocarbon ages from terrestrial and aquatic macrofossils yield basal ages of 10,700 ¹⁴C yr B.P. for the deep core and 8,800 ¹⁴C yr B.P. for the shallow core, showing that the lake was at least >4 m lower than modern during this interval. Radiocarbon based age models indicate that this was also a period of relatively rapid sediment accumulation. The White River Ash (1230 ¹⁴C yr B.P.) is 1-cm thick in both the deep core and intermediate core, but is entirely missing from the shallow core, indicating that lake-level was between 2 to 4-m lower than modern during that time. Lithologic variations of the shallow core marl suggest additional lake-level changes of 1 to 2-m during the middle and late Holocene.